Additives for the manufacture of glass

ABSTRACT

A glass additive composition which consists of a carrier such as calcium carbonate, having an active material such as zinc selenite in combination with a surfactant and/or film forming material deposited thereon is an effective medium for introducing active materials into the glass manufacturing process and especially the manufacture of container glass.

FIELD OF THE INVENTION

This invention relates to additive compositions for use in themanufacture of glass, to methods for their preparation and to glassmanufacturing processes using such additives.

BACKGROUND OF THE INVENTION

In the manufacture of glass, batch materials such as sand, soda ash, andlimestone etc are combined with various additives such as colorants ordecolorisers, and subjected to extremely high temperatures to melt thematerials. During this high temperature melting process, a portion ofsome of the solid materials volatilise when being converted to theglassy liquid state. Such volatilised materials may exit out through thefurnace exhaust system with other gases and hence are essentially lostfrom the glass melt. Apart from being volatilised, the additives mayalso be lost from the process in particulate form as dust, which isblown through and from the furnace during the process.

This unwanted removal of additive material, which is a vital part of thefinal glass product, requires that excess quantities of the additivematerial must be included in the batch to ensure that the final productcontains the desired amount of the additive.

The unwanted loss of additive materials in this fashion leads toincreased raw material costs in glass manufacture. In addition extraexpense may be incurred, as it may be necessary to prevent additivematerials from the furnace exhaust being emitted into the atmosphere.Also, many additive materials in their volatile form are corrosive tocertain refractory materials used in the glass manufacturing process.Therefore, it is desirable to improve the retention of additivematerials within the glass manufacturing process and the final product.

An example of one highly volatile component employed in some glasscompositions, such as container glass manufacture, is selenium, which isoften used in combination with cobalt as a decolouriser. When seleniumis added to the glass batch as elemental selenium, about 75 to 80% isconverted to the gaseous state and hence essentially 75-80% of the addedselenium is vaporised out of the glass batch and is lost as dust orfume.

The loss of up to 80% of any additive material represents a significantwaste of an expensive raw material in the process. In addition someadditive materials in their volatile form may be toxic e.g. selenium,and any loss from the process presents a potential hazard to human andanimal health. Because the exact loss from the process is not accuratelypredictable, it may also be difficult to maintain the quality of theglass and control the relative ratios of additive components, such asfor example the ratio of selenium to cobalt, in the final glass product,this is therefore an inefficient process.

Various approaches have been used in the art to overcome the problems ofretention of volatile additives such as selenium during glassmanufacture. One approach is the utilisation of glass frits oragglomerates which contain high levels of the volatile additive in anamorphous (glassy) state which makes it more difficult for any volatilecomponents to leave the glass batch composition during melt processing.This approach has been proposed in WO96/07621, GB 1,036,477, U.S. Pat.No. 2,955,948, U.S. Pat. No. 3,291,585, and U.S. Pat. No. 3,628,932.Another approach proposed in the art is the use of encapsulation asdescribed in EP 0 618 177 A1.

Many processes using selenium as a colorant/decolourant have alsoincluded sodium nitrate or potassium nitrate in the batch mixture tohelp improve the retention of selenium in the final product or for otherpurposes. For example, U.S. Pat. Nos. 3,296,004; 4,101,705; 4,104,076;and 4,190,452 all disclose bronze glass compositions using seleniumtogether with sodium or potassium nitrates as components of their glassbatches.

U.S. Pat. No. 4,104,076 teaches the addition of selenium and nitrates tothe batch to make a grey glass composition as well as a bronze glasscomposition. U.S. Pat. No. 5,070,048 teaches a blue coloured glassproduct made using selenium together with sodium nitrate in the batchmixture. U.S. Pat. Nos. 4,339,541; 4,873,206; 5,023,210; 5,308,805;5,346,867; 5,411,922; and 5,521,128 all teach the use of sodium orpotassium nitrate in the batch when selenium is used as a colorant tomake grey glass products. Hence, as seen from the above, it is extremelycommon in the glass making industry to include nitrates when usingselenium as a colorant.

In the context of coloured glass, other approaches to reduce the use ofnitrates have utilised oxidising agents and reducing agents to improveselenium retention such as described in GB 2,260,978 or alternativelymanganese oxide as described in U.S. Pat. No. 5, 346,867 and WO99/29634.

Selenium has been utilised in many forms for the manufacture of glass.Elemental selenium occurs in two forms, the red form being converted tothe grey form at 130° C. The grey form of selenium melts at 217° C. andboils at 688° C. Under glass melt conditions, which may be as high as1450° C., selenium is converted to oxygen compounds and polyselenidesand may be present in a number of oxidation states as the selenide,selenate or selenite. In view of the volatility of elemental seleniumother compounds of selenium with higher melting and/or boiling pointshave been proposed. One such class of selenium compounds are theselenites, including sodium selenite, calcium selenite, barium selenite,magnesium selenite and zinc selenite. However, these selenite materialsare difficult to handle and control during glass manufacture. Sodiumselenite is hygroscopic and cakes on storage making it difficult toproduce homogeneous mixtures for processing. A further problem withselenite salts is that soluble salts are more harmful compared toselenium metal due to their solubility. In addition selenium salts havea small particle size, which increases losses during use in the exhaustfrom the process as particulate dust.

Many forms of selenium and cobalt, as used in the glass manufacturingprocess, exhibit a propensity to form dust. All components ofparticulate blends have a propensity to form dust. This propensity willdepend on: the magnitude of the force applied to the mixture; thephysical characteristics of each component, of which, particle size,particle shape, electrostatic properties, particle surface profile andmoisture content, are particularly important; and the physicochemicalinteractions that occur between the individual particles of thedifferent components of the mixture. Additive materials may be emittedfrom blends in dust and the levels of the additive material in the dustmay be lower or higher than the level in the original processing mass.To describe this phenomenon the term Propensity to Dust (PD) is used andis broadly defined as follows:PD=(% component in the dust)+(% component in the processing mass)

Dust emissions can be determined by a number of methods well known inthe art, such as the method devised by Stauber using the HeubachDustmeter (Ref. Fresenius Z. Anal. Chem.(1984), 318, 522-524, the wholecontents of which is hereby incorporated by reference). Ideally onewould wish to provide formulations which reduce the propensity to dustfor important or hazardous components. The formation of dust ishazardous and also contributes to the loss of these additives from theglass making process as dust emissions.

Apart from the volatilisation of glass additives, a further problem isoften observed in the manufacture of the glass batch. This is theproblem of segregation or classification within the batch, which occursduring its manufacture and/or introduction to the furnace. The variouscomponents used in the manufacture of glass batches may havesignificantly varying particle sizes, particle size distributions,particle shapes, densities and surface characteristics. This relativelywide variation in particle properties often results in segregationmaking it difficult to produce glass batches of uniform composition forintroduction into the furnace. This segregation may occur as the batchmaterials are transferred around the glass manufacturing plant. It mayalso occur during the actual point of feeding the glass batch materialinto the process as vibration feeders are often used at this stage.

An additional problem occurs on introduction of the batch to the glassfurnace; particles of material maybe purged from the batch before itenters the glass melt. This purging effect is due to the action of hotair, which is blown through the glass furnace and out to exhaust,selectively removing smaller particles and low-density particles fromthe batch as it is being introduced to the process. The overall effectis that significant quantities of additive materials may be removed fromthe process in this way and be lost in the exhaust.

A further difficulty is observed when attempts are made to introduce lowlevels of an additive into the glass manufacturing process. It issometimes difficult or almost impossible to introduce the additive intothe process in a controlled fashion to ensure uniformity in the glassbatch or uniformity of the finished product. This is especiallydifficult when automated weighing systems are used. The dosing ofselenium/cobalt is not generally a problem as the combination isintroduced as a premix. However, the problem may be acute when a singleadditive such as cerium is added to the process, partly because ceriumneeds to be added in relatively small quantities.

Selenium is such a strong colourant that it has been used in glasscompositions at concentrations as low as 0.0002 to 0.0035 weight % toimpart a strong absorption in the spectral transmission between 400 and500 nanometres. Such low levels are difficult to meter accurately intothe glass manufacturing process. The additive composition of the presentinvention is an effective form for introducing selenium into a glassmanufacturing process in a controlled manner.

An object of the present invention is to provide a new means ofintroducing additive materials often as trace inclusions into the glassmanufacturing process. This is achieved by the use of an additivecomposition that enables the more effective introduction of additivematerials into the glass manufacturing process and more especially intoa process for the manufacture of container glass.

The present invention seeks to reduce the problem of segregation whenintroducing additive materials into glass batches and/or the problem ofthe loss of these additive materials through volatilisation or dustformation during the glass manufacturing process. The present inventionalso provides a means of introducing additives to the glassmanufacturing process in a controlled and effective manner.

SUMMARY OF THE INVENTION

The present invention therefore in a first aspect provides a particulateglass additive composition comprising at least one particulate carrierand, deposited on the surface of the carrier or carriers, at least oneglass additive material in combination with a matrix, the matrixcomprising at least one surface-active agent or at least one organicfilm forming material or mixtures thereof.

In a second aspect the present invention provides a process for themanufacture of a particulate glass additive composition which processcomprises contacting at least one particulate carrier with at least oneglass additive material to provide a coated carrier followed by contactof the coated carrier with one or more surface-active agents or one ormore organic film forming materials or mixtures thereof to form amatrix.

In a third aspect the present invention provides a process for themanufacture of a particulate glass additive composition which processcomprises mixing at least one glass additive material with one or moresurface-active agents or one or more organic film forming materials ormixtures thereof to form a mixture, followed by contacting of themixture with one or more particulate carriers to form a coating of themixture thereon.

In a fourth aspect the present invention provides a process for themanufacture of a particulate glass additive composition which processcomprises contacting at least one particulate carrier one or moresurface-active agents or one or more organic film forming materials ormixtures thereof to provide a treated carrier followed by contacting ofthe treated carrier with one or more glass additive materials.

In each of the aspects two to four the process steps may be repeated tobuild up the amount of glass additive material incorporated into theparticulate glass additive composition.

In a fifth aspect the present invention provides a process for themanufacture of glass which process comprises introducing at least oneparticulate glass additive composition according to the invention intoglass forming components to form a glass batch before introduction to amelting furnace or which process comprises introduction of at least oneparticulate glass additive composition according to the inventiondirectly into the melting furnace during molten glass formation.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a new form of additive composition forthe introduction of various elements, compounds or materials into theglass manufacturing process. The additive composition has a specificformulation of components and specific methods of manufacture, whichenables the additive composition to be the effective means ofintroducing additive materials to the glass manufacturing process. Thecomposition has as its key elements a particulate carrier, an additivematerial, and a surface-active agent and/or organic film formingmaterial.

The particulate carrier may be organic or inorganic and may have anyphysical shape; it is preferred that it is substantially spheroid inshape. When the carrier is organic it may be derived from syntheticorganic materials such as organic hydrocarbon polymers or it may bederived from natural organic materials such as corn-cobs or hazelnutshells. It is preferred that the organic particulate carrier is agranular particulate material derived from an organic polymer. Theorganic material must be such that it is consumed e.g. via oxidation,under glass manufacturing conditions so that substantially no residue ofthe organic material remains in the finished glass product. A residuemay be tolerated if it does not significantly detract from the qualityof the glass product.

In a preferred embodiment the particulate carrier is an inorganicmaterial. The particulate inorganic carrier may be any inorganicmaterial, which is compatible with the glass manufacturing process. Itmaybe a material that is a major pre-cursor for the final glass productand is therefore consumed in the process in order to form the glass. Theinorganic carrier may be a material that, whilst not being consumed toform glass, has substantially no detrimental effect on the physicalproperties of the final glass product. Non-limiting examples of suitableinorganic materials when in particulate form include lead oxide, zincoxide, boron oxide, sulphates, fluorides, chlorides, bromides, iodides,phosphates, calcium carbonate, and suitable mixtures thereof. A furthersuitable carrier is ground glass. A preferred particulate inorganiccarrier is calcium carbonate. One example of suitable calcium carbonateis Longcliffe Calcium Carbonate P10 which is obtained from very highpurity carboniferous limestone; this material has a moisture content of<0.1 wt %, a specific surface area of greater than 0.2 m²g⁻¹ (typically0.24 m²g⁻¹) and a particle size (at least 97%) within the range 0.6 to1.7 mm. Other examples of suitable calcium carbonates include Trucal 14®and Trucal 25® manufactured by Tarmac Central Ltd; both of thesematerials have low water contents of less than 0.05 wt % and particlesize (at least 99%) within the range 75 um to 2.36 mm. It is importantthat at least 98 wt % of the material has a particle size of 150 um orgreater. In the case of Trucal 14® only 0.9 wt % of the material has aparticle size below 600 um. It is preferred that the maximum particlesize is 4.5 mm. It is preferred that when the additive composition isfor use in tank furnaces that 1 wt % or less of the calcium carbonate inthe additive is of particle size 3.35 mm or above. When the additivecomposition is to be used in a pot furnace it is preferred that thereare no particles greater than 3.35 mm and that 5 wt % or less are ofparticle size greater than 1 mm.

The preferred chemical composition of the calcium carbonate is asfollows: the calcium content expressed as calcium oxide, CaO, ispreferably not less than 55.2 wt % (this is equivalent to a calciumcarbonate purity of 98.5 wt %); the total iron content expressed asferric oxide (Fe₂O₃) should preferably not exceed 0.035 wt %; the totalnon-volatile matter insoluble in hydrochloric acid should preferably notexceed 1.0 wt %; the organic matter should preferably not exceed 0.1 wt%; and the colouring elements, other than iron, should preferably not bepresent to an extent sufficient to produce a colour in the glass.

The mass, size, shape and surface properties of the particulate carrierare selected to be compatible with the glass additive material ormaterials to be used, the surface-active agent or agents to be used andthe glass manufacturing process. The particulate carrier must have therequired physico-chemical characteristics to ensure that any particularcombination of additive and surfactant is retained on its surface.Important characteristics to be considered include its electrostaticcharacter, its surface morphology and its hydrophobic/hydrophilicbalance. Thus, for certain additive materials it may be necessary toselect a particulate with a certain surface charge to ensure that theadditive material is attracted to the carrier surface during preparationof the additive composition. Also, a particulate carrier with a highsurface area may be beneficial in achieving a high loading of additivematerial, when required, on the surface of the carrier. It is preferredthat the particle size of the carrier is 150 microns or greater.

The glass additive material used in the manufacture of the additivecomposition of the present invention may comprise one or more materialsthat are added to the glass formulation in addition to the normal bulkcomponents in order to modify the properties of the basic glasscomposition. The bulk components often used in the preparation of aglass batch, and which are key components of the finished glass itself,are not generally additive materials according to the present invention.These bulk components include network formers, intermediates, networkmodifiers, and cutlet; these materials are described in detail in “RawMaterials for Glass Making—A Review”, F. G. West-Oram, Glass Technology,Vol 20, No. 6, December 1979, pages 222-245. Examples of these bulkcomponents include silica, sodium oxide, calcium oxide, magnesium oxideand alumina.

The glass additive materials are typically utilised as minor componentsof the glass and often as a trace addition to the glass manufacturingprocess. Typical examples of such additives include materials that areincorporated at low levels to modify the colour of the glass; thesematerials are often referred to as colourants or decolourants. Thesematerials should be distinguished from primary colouring bodies, whichare used to introduce and impart the primary colouring agents forglasses and enamels. Other additive materials include oxidants, reducingagents, nucleation catalysts, accelerating and refining agents. They mayalso include materials normally designated as bulk materials but whichfor some forms of glass are introduced as a minor or trace component ofthe glass. These materials are described in detail in “Raw Materials forGlass Making—A Review”, F. G. West-Oram, Glass Technology, Vol 20, No.6, December 1979, pages 222-245.

The glass additive material may be a material that is not normally usedin the manufacture of glass or may be in a form that is not typicallyused in glass manufacture. Thus, the additive material may be anon-typical chemical source of one or more elements that are beneficialin glass manufacture. In this context the additive composition andprocess of the present invention is particularly effective in enablingdifficult to handle materials, such as hygroscopic materials, to be usedas the additive material.

It is preferred that the additive material has a melting point of 200°C. or greater. The additive composition and process of the presentinvention are of particular benefit when used to introduce sources ofdecolourising agents such as selenium into the glass manufacturingprocess. Thus selenium as additive material may be utilised in theprocess of the present invention as the metal element or as a compoundof selenium. Suitable compounds of selenium include the selenides,polyselenides, selenites, or selenates. Examples of suitable selenitesinclude sodium selenite, calcium selenite, barium selenite, magnesiumselenite and zinc selenite. It is most preferred that the additivematerial comprises one or more sources of selenium and more preferablycomprises at least one selenite and most preferably comprises zinc orsodium selenite. It is preferred that the selenite has low levels ofiron that is less than 200 ppm. More preferably the iron content is 50ppm or less and most preferably 20 ppm or less. One particularlysuitable selenite is zinc selenite with an iron content of 10 ppm orless. Examples of such zinc selenites are Zinc Selenite Type I (300 um)and Type II (150 um) manufactured by Retorte (Ulrich Scharrer GmbH).Both of these materials contain at least 41 wt % selenium.

In addition the additive composition and process of the presentinvention is also effective for the introduction of cobalt into glassmanufacturing processes. Cobalt is often used in combination withselenium as decolourising agent for container glass or flint glassmanufacture. Selenium is an important additive to correct for thenegative effects of Fe in the glass. In these processes the quantity ofcobalt required is linked to the amount of selenium introduced into theglass melt. Thus both the required amounts of selenium and cobalt aredependent directly or indirectly on the trace element concentrations ofmaterials such as Fe. When cobalt compounds are included in the additivecomposition of the present invention in combination with the selenium onthe same particulate, it is possible to more accurately and effectivelycontrol the combined amounts of selenium and cobalt as required toachieve the optimum decolorisation of the finished glass. Thus in afurther aspect the processes for the manufacture of additivecompositions according to the second, third and fourth aspects furtherinclude the addition of a source of cobalt. This addition may occur atthe same time as the selenium or at a different stage of the process. Itis possible to prepare the selenium based additive composition and thecobalt based additive composition separately and then to combine the twoadditive compositions to provide a formulated composition. The preferredform of cobalt is the black oxide (70 to 72% cobalt). Other preferredadditive materials or co-additive materials include compounds of Ce,especially Ce³⁺, Cr, Ag, Au, As, Mn, Cu, Sb, Fe, Ti, S, Cd, Ni, Te, Geand the Rare Earths (lanthanides). Manganese compounds may be usefullyincorporated into the additive composition comprising selenium to enablethe use of lower levels of selenium. Non-limiting examples of additivematerials include CO₃O₄, CU₂O, CuO, Mn₂O₃, NiO, Cr₂O₃, V₂O₃, MoO₃, MnO,TiO₂, CeO₂, Na₂S, CdS, UO₃, CdS, Sb₂S₃, and CO₃O₄.

The additive material may be used in any form that is compatible withthe processes used for manufacture of the additive composition. Thus itmay be utilised in the form of a liquid, solution, dispersion, or insolid particulate form. It is preferred that the additive material isused in the solid particulate form. In this form it is preferred thatthe particle size is as small as possible and is in any event less than300 microns. When the additive material is cobalt oxide it is preferredthat 100% of the particles have a particle size of less than 200microns. When the additive material is a selenite e.g zinc selenite, itis preferred that the particle size is less than 300 micron and morepreferably less than 200 micron. In a preferred embodiment the zincselenite has a particle size distribution as follows: 100% of theparticles are of particle size of less than 300 micron, 98% of particlesize of less than 150 micron, 90% of particle size of less than 75micron and 70% of particle size less than 45 micron. It is preferredthat the additive material has at least 70% of the particles of particlesize less than 100 micron, more preferably less than 75 micron and mostpreferably less than 50 micron.

The surface-active agent may be any surface-active agent that iscompatible with the carrier, the additive material and the glassmanufacturing process. It effectively binds or holds the additivematerial onto the surface of the carrier. Suitable surface-active agentsinclude non-ionic surfactants, anionic-surfactants andcationic-surfactants. Suitable non-ionic surface agents includemonoesters of propyleneglycol and of the food fatty acids,stearyl-2-lactylic acid, acetic, lactic, citric, tartaric andmonoacetyltartaric esters of the mono and diglycerides of food fattyacids, glycerin polyethyleneglycol ricinoleate, polyethyleneglycolesters of soybean oil fatty acids, sorbitan monostearate sorbitantristearate, sorbitan monolaurate, sorbitan monooleate, sorbitanmonopalmitate and propyleneglycol alginate. Mixtures of thesesurface-active agents with polyethyleneglycol and/or withpropyleneglycol and/or with glycerin can also be used. One example of asuitable surfactant combination is 10 parts Polysorbate 20 (Tween 20®)and 1 part polyethyleneglycol 300. Other suitable surfactants includeCremophor EL® which is a polyoxyethylenglyceroltriricinoleat 35 (DAC)and is manufactured by BASF.

In place of or in addition to the surfactant is used an organic filmforming material. Preferably this is an organic polymer which as part ofthe matrix. It is preferably a thin layer of water-soluble orwater-dispersable preferably non-toxic polymer which forms a film at atemperature less than 60° C.

The use of this organic film forming material and/or surfactant ensuresthat the glass additive material remains in contact with and bound tothe carrier material and has no possibility of separating from thecarrier and coming into contact with other components of the glassmixture during the subsequent processing in the glass manufacturingprocess.

Polymers suitable as the organic film forming material include forexample cellulose derivatives such as: methylcellulose,hydroxypropylcellulose, methylhydroxypropylcellulose,hydroxypropylmethylcellulose (HPMC), cellulose acetate phthalate (CAP),carboxymethylcellulose, ethylcellulose and acetylcellulose,Hydroxypropylethylcellulose (HPEC) and mixtures of microcrystallinecellulose and carrageenan), vinyl polymers (polyvinylpyrrolidone,polyvinyl alcohol and polyvinylacetate), gum arabic, substances of waxtype such as polyethyleneglycols, higher alcohols, higher fatty acidsand hydrogenated fatty substances. Other suitable materials includexantham gum, dextrins and maltodextrins.

Preferably the surface-active agent and or organic film forming materialis present in a quantity of between 1 and 10% by weight with respect tothe combined weight of the carrier and additive material, morepreferably 2 and 8%.

The choice of surface-active agent and/or film forming material is basedon the hydrophilic and/or lipophilic characteristics of the carrierand/or the additive material. They may be introduced into the process byspraying, pouring, or dripping. Some surface-active agents may be solidsor waxy materials under ambient conditions; these may be introduced tothe process as a melt to the solid mixture of carrier and additivematerial. If the solid mixture is cooler than then melted surfactantthen this will assist in solidifying the surface-active agent on thesurface of the carrier coated with additive material. Alternatively, themixture may be cooled after addition of the surfactant melt to ensuresolidification on the carrier surface. It is also possible to introducethe surface-active agent to the mixture in the solid form and to inducemelting of the surfactant in situ under the mixing conditions used. Inone embodiment the surface-active agent is applied by spraying into thesolid mixture of carrier and additive material whilst this solid mixtureis under mixing conditions.

The additive material especially when in the form of a particulate maybe applied to the carrier by mixing in a solids mixer. The quantity ofapplied additive is between 1 and 80%, preferably between 1 and 60%, andmost preferably between 1 and 45% by weight with respect to the weightof carrier and surfactant. More preferably it is within the range of 2to 10% by weight with respect to the combined weight of carrier andsurfactant. This is the preferred range especially when the additivematerial is a selenite such as sodium or zinc selenite. When theadditive material is manganese oxide the preferred range is 1 to 40 wt%. When the carrier is calcium carbonate and the additive material iszinc selenite it is preferred that the quantity of additive is withinthe range 1 to 30% by weight the combined weight of carrier andsurfactant. The amount of selenite is selected to provide the requiredlevel of selenium in the final additive composition. Preferably theamount of active additive e.g. selenium and/or cobalt, present in thefinal additive composition is within the range of 0.25 to 35% and morepreferably within the range of 1 to 20% and most preferably within therange of 2 to 15% by weight based on the total weight of the additivecomposition.

In a preferred embodiment the glass additive composition is provided ina glass batch composition which comprises in addition to the additiveone or more glass precursor materials.

The process as described in the third aspect of the present invention isthe preferred process for the manufacture of the glass additivecomposition of the present invention and generally consists of thefollowing steps. Firstly, the requisite amount of carrier is introducedinto a mixing vessel. Then the requisite amount of surfactantcomposition is added to the carrier material in the mixing vessel withcontinuous or intermittent mixing, preferably with continuous mixing,until an even fluid dispersion is obtained. Once this even dispersion isobtained the requisite amount of particulate additive material isintroduced to the mixing vessel in stages with continued mixing. As theparticulate additive material is introduced the mixture gradually takeson the form of granules. This granulated product is the additivecomposition of the present invention.

For some formulation it is beneficial to include an oil into theprocess; this may assist in the granule formation and ensure that all ofthe additive material is incorporated into the matrix on the carrier.Examples of a suitable oil include mineral oils, white oil, vegetableoil and spreading oils.

In addition a flow aid may also be added to the mixture. If the granulehas a relatively high content of water the flow aid assists with themixing and processing and aids the flow properties of the granulatedmixture. One suitable flow aid is hydrophobic silica.

The additive compositions of the present invention may be utilised inthe manufacture of many different types of glass. The glass batch of thepresent invention may comprise one or more additive compositionsaccording to the present invention. Preferably when two additivecompositions are used one comprises selenium and the second comprisescobalt. A typical process for the manufacture of container glass isshown schematically in FIG. 1.

In this process the additive composition (1) is first prepared ready forintroduction into the process. This additive composition may then ifnecessary be batch blended with other materials to form a decolourisingpremix (2). If the additive composition (1) already comprises all therequired decolourising materials then the premix stage (2) may beomitted and the additive composition (1) may be introduced directly tothe glass batch weighing stage (4). At the glass batch weighing stage(4) the additive composition (1) or the premix (2) are combined with thebulk glass raw materials (3) in the requisite proportions to obtain therequired glass composition from the glass furnace. The weighedcomponents are then transferred to a glass batch blending stage (5)where all the components are thoroughly blended prior to introduction tothe glass furnace (6).

A large variety of glasses with different chemical and physicalproperties can be made by a suitable adjustment to compositions used intheir manufacture. The main constituent of most commercial glasses issand. Sand is formulated with other chemicals for ease of processing andin order to achieve the desired properties in the final glass product.The addition of sodium carbonate (Na₂CO₃), known as soda ash, in aquantity to produce a fused mixture of 75% silica (SiO₂) and 25% ofsodium oxide (Na₂O), will reduce the temperature of fusion to about 800°C. However, a glass of this composition is water-soluble and is known aswater glass. In order to give the glass stability, other chemicals likecalcium oxide (CaO) and magnesium oxide (MgO) are needed. The rawmaterials used for introducing CaO and MgO are their carbonates CaCO₃(limestone) and MgCO₃ (dolomite), which when subjected to hightemperatures give off carbon dioxide leaving the oxides in the glass.

An important class of glass is container glass. This is typicallyderived from a soda-lime silica glass with a typical composition byweight of SiO₂ 74%, Na₂O 14%, CaO 11%, and Al₂O₃ 1%. For certaincontainer glasses where clarity and colour are important furtherchemical additives are introduced into the process to aid incolour/clarity control. It is preferred that the additive composition ofthe present invention is used in the manufacture of glasses, whichrequire the addition of selenium and/or cobalt, and especially containerglass.

The majority of commercial glasses used for the manufacture of containeror flat glass are based on compositions that fall within the rangesidentified in Table 4.

The raw materials within the composition are carefully weighed andthoroughly mixed, as consistency of composition is important. Inaddition glass cullet may be added to the composition; from 10 to 70% or10 to 80% of the composition may be glass cullet.

Examples of suitable container glass batch formulations, which may beused in the glass manufacturing process of the present invention, areprovided in Tables 2 and 3. Typical ranges of components for thesecontainer glass batches are provided in Table 4.

Flat glass is similar in composition to container glass except that itcontains a higher proportion of magnesium oxide. A typical flat glasscomposition by weight is SiO₂ 71%, Na₂O 16%, CaO 9%, Al₂O₃ 1% and MgO3%.

Generally, in forming selenium containing glasses according to thepresent invention raw material components would most generally comprisecomponents like sand, soda ash, dolomite, limestone, salt cake, rouge(for iron oxide colorant), a manganese containing compound, and seleniumcompound. The amounts and the particular materials employed woulddepend, however, on the particular glass being produced and selectionwould be within the skill of one in the art in view of the presentdisclosure.

The additive composition of the present invention may be used as a meansof introducing trace elements and compounds into any glass. Most of theglasses produced commercially on a large scale may be classified intothree main groups: soda-lime, lead and borosilicate, of which the firstis by far the most common. However, the invention is also appropriatefor the manufacture of specialist glasses, which require theintroduction of trace inclusions or even relatively high levels ofselenium and/or cobalt. TABLE 2 Nepheline Norwegian Formulation SandSoda Ash Limestone Dolomite Saltcake Syenite Calumite Carbon FeldsparAlumina A 1000 266.7 180.4 114.6 11.4 25.0 60.0 B 1000 318.6 224.9 10.519.9 70.6 C 1000 310.4 224.4 39.6 11.7 56.5 41.3 D 1000 293.3 290.0 28.393.3 E 1000 318.6 224.9 10.5 19.9 70.6 F 1000 315.7 242.5 35.3 10.5 56.962.1 G 1000 313.8 257.1 13.2 9.0 11.4 71.7 H 1000 313.5 257.8 13.2 10.711.5 71.9 2.8 I 1000 266.7 180.4 114.6 11.4 25.0 60.0 J 1000 320.5 300.450.6 8.2 7.7 71.8 K 1000 301.4 237.1 12.9 48.6 60.0 L 1000 293.6 198.990.9 10.8 64.0 47.4 M 1000 310.0 177.0 85.0 9.2 68.0 N 1000 311.3 222.712.3 44.7 70.0 O 1000 293.6 198.9 90.9 10.8 64.0 47.4 P 1000 301.1 127.6143.7 16.0 16.6 Q 1000 309.7 216.2 120.8 9.9 55.4 R 1000 307.7 259.6 9.944.2 16.8 S 1000 303.7 217.8 50.7 11.9 27.2 51.5 0.2 6.7 0.9

All Figures are weight in Kg TABLE 3 Nepheline Norwegian FormulationSand Soda Ash Limestone Dolomite Saltcake Syenite Calumite CarbonFeldspar Potash A1 1000 312.9 265.9 20.65 61.29 B1 1000 278.7 191.553.99 10.38 41.53 12.87 C1 1000 301.1 133.3 134.97 10.38 41.53 47.76 D11000 282.4 191.9 56.89 10.38 41.53 16.61 E1 1000 303.2 240.5 7.29 81.6354.66 F1 1000 307.1 237.1 13.46 39.58 60 G1 1000 308.3 237.1 11.38 39.5860 H1 1000 304.9 205.2 93.93 10.84 65.03 40.46 I1 1000 315.4 188.0 83.7610.26 17.09 52.14 J1 1000 296.7 286.7 11.67 70 0.29 K1 1000 309.8 296.87.87 57.77 0.29All Figures are weight in Kg

TABLE 4 Component of Glass Batch Range in weight percent Sand   56 to 66SodaAsh   16 to 20 Limestone   7 to 18 Dolomite   0 to 9 Saltcake 0.25to 2 Nepheline Syenite   0 to 5.5 Calumite   0 to 4.5 Carbon   0 to 0.3Norwegian Feldspar   0 to 4 Aluminium   0 to 17 Potassium   0 to 3.5

Lead glasses are based on the use of lead oxide instead of calciumoxide, and of potassium oxide instead of all or most of the sodium oxidein soda-lime glasses. The traditional English full lead crystal containsat least 30% lead oxide (PbO) but any glass containing at least 24% PbOcan be legitimately described as lead crystal according to the relevantEEC directive. Glasses of the same type, but containing less than 24%PbO, are known simply as crystal glasses. Glasses with even higher leadoxide contents (typically 65%) may be used as radiation shieldingglasses because of the well-known ability of lead to absorb gamma raysand other forms of harmful radiation.

Borosilicate glasses are composed mainly of silica (70-80%) and boricoxide (7-13%) with smaller amounts of the alkalis (sodium and potassiumoxides) and aluminium oxide.

Silica glass or vitreous silica is of considerable technical importance.However, the fact that temperatures above 1500° C. are necessary in themelting makes the transparent variety (often known as fused quartz orquartz glass) expensive and difficult to produce. The less expensivealternative for many applications is fused silica, which is melted atsomewhat lower temperatures; in this case small gas bubbles remain inthe final product, which is therefore not transparent. Anothersubstitute for vitreous silica can be produced by melting a suitableborosilicate glass and then heating it at around 600° C. until itseparates into two phases. The alkali-borate phase may be leached outwith acids, leaving a 96% silica phase with open pores of controllablesize, which can be converted, into clear glass. Porous glasses of thiskind, commonly known as Vycor, from the first commercial versionproduced by Corning Glass Works Ltd, may be used as membranes forfiltration purposes and for certain biological applications.

Aluminosilicate glasses contain 20% aluminium oxide (alumina-Al₂O₃)often including calcium oxide, magnesium oxide and boric oxide inrelatively small amounts, but with only very small amounts of soda orpotash. They tend to require higher melting temperatures thanborosilicate glasses and are difficult to work, but have the merit ofbeing able to withstand high temperatures and having good resistance tothermal shock.

Alkali-barium silicate glasses contain small amounts of heavy oxides(lead, barium or strontium).

Borate glasses are a range of glasses, containing little or no silicathat can be used for soldering glasses, metals or ceramics at relativelylow temperatures. When used to solder other glasses, the solder glassneeds to be fluid at temperatures (450°-550° C.) well below that atwhich the glass to be sealed will deform. Some solder glasses do notcrystallise or denitrify during the soldering process and thus themating surfaces can be reset or separated; these are usually lead borateglasses containing 60-90% PbO with relatively small amounts of silicaand alumina to improve the chemical durability. Another group consistsof glasses that are converted partly into crystalline materials when thesoldering temperature is reached, in which case the joints can beseparated only by dissolving the layer of solder by chemical means. Suchdenitrifying solder glasses are characterised by continuing up to about25% zinc oxide.

Glasses of a slightly different composition (zinc-silicoborate glasses)may also be used for protecting silicon semi-conductor componentsagainst chemical attack and mechanical damage. Such glasses must containno alkalis (which can influence the semi-conducting properties of thesilicon) and should be compatible with silicon in terms of thermalexpansion. These materials, known as passivation glasses, have assumedconsiderable importance with the progress made in microelectronicstechnology in recent years that has made the concept of the “siliconchip” familiar to all.

Phosphate are known as semi-conducing oxide glasses and are usedparticularly in the construction of secondary electron multipliers.Typically they consist of mixtures of vanadium pentoxide (V₂O₅) andphosphorous pentoxide (P₂O₅). Chalcogenide glasses offer similar semiconductor effects and can be made without the presence of oxygen(non-oxide glasses). These may be composed of one or more elements ofthe sulphur group in the Periodic Table combined with arsenic, antimony,germanium and/or the halide (fluorine, chlorine, bromine, iodine).

Other glasses include optical glasses. Glasses with high dispersionrelative to refractive index are called flint glasses while those withrelatively low dispersions are called crown glasses. Typically flintglasses are lead-alkali-silicate compositions whereas crown glasses aresoda-lime glasses. The substitution of other oxides permits considerablevariations to be achieved. Thus barium crown (barium borosilicate),barium flint (barium lead silicate), borosilicate crown (sodiumborosilicate) and crown flint (calcium lead-silicate) are all widelyused. Phosphorous and the rare earths, especially lanthanum, may also bevaluable ingredients in some optical glass compositions. The inclusionof transition elements (copper, titanium, vanadium, chromium, manganese,iron, cobalt or nickel) in glass produces strong absorption bands in theultra violet part of the spectrum as well as broad bands in the visibleand infra-red, enabling a series of colour filters and glasses withmodified transmission properties in the ultra-violet and infra-red to beproduced.

The use of rare earths has less effect on colour but it is of particularsignificance in the manufacture of laser glasses, most of which containneodymium. The neodymium ions in the glass, when stimulated, emitradiation at a particular wavelength (1.06 um) and this is transformedinto high-intensity coherent optical data, and for various measurementfunctions in industry.

Other glasses are the photochromic glasses, which include in theircomposition silver halide crystals produced by adding silver salts andcompounds of fluoride, chlorine or bromine (the halides) to thebase-glass (normally borosilicate). Controlled thermal treatment duringand after melting causes extremely small phase separations to occur andthese are responsible for the reversible darkening effect.

A further class of glasses are the sealing glasses, which may be usedfor sealing to tungsten, in making incandescent and discharge lamps,borosilicate alkaline earths-aluminous silicate glasses, are suitable.Sodium borosilicate glasses may be used for sealing to molybdenum andthe iron-nickel-cobalt (Fernico) alloys are frequently employed as asubstitute, the amount of sodium oxide permissible depending on thedegree of electrical resistance required. With glasses designed to sealto Kovar alloy, relatively high contents of boric oxide (approximately20%) are needed to keep the transformation temperature low and usuallythe preferred alkali is potassium oxide so as to ensure high electricalinsulation.

Other glasses which may be manufactured according to the process of thepresent invention include architectural glasses and automobile glassessuch as grey glasses, which typically have a composition by weight ofSiO₂ 68 to 75%, Al₂O₃ O to 5%, CaO 5 to 15%, MgO O to 10%, Na₂O 10 to18%, and K₂O O to 5%.

In addition, the colouring components of the grey glass compositionconsist essentially of: 0.9 to 1.9 wt. % total iron oxide as Fe₂O₃, 0.10to 1.0 wt. % manganese oxide as MnO₂; 0.002 to 0.025 wt. % cobalt oxideas Co, and 0.0010 to 0.0060 wt. % selenium as Se, and 0 to 1.0 wt. %titanium oxide as TiO₂. The glass may also include tramp materials,which sometimes enter the glass with raw materials or as a result ofchangeover of one glass composition to another in a glass furnace. Forexample, this would include up to about 0.005 wt. % nickel oxide as NiO.

The manganese compound is employed to provide in the glass an amount of0.10 to 1.0 wt % manganese oxide based on MnO₂, more preferably being0.15 to 0.8 wt. %, most preferably being 0.15 or 0.20 to 0.60 MnO₂. Thismanganese compound colorant can be added to the batch glass componentsin a variety of forms, for example, but not limited to, MnO₂, Mn₃O₄,MnO, MnCO₃, MnSO₄, MnF₂, MnCl2, etc. Preferably it is most desirable touse the manganese oxide or manganese carbonate compounds in the batch.As would be appreciated, a mixture of such compounds may also beemployed. In the glass composition, this colorant is generally presentin the Mn⁺² and Mn⁺³ state, although it may additionally be present inother states such as Mn⁺⁴.

Manganese oxide when added to the glass batch materials replaces aportion of the selenium decolourant/colorant and in the specifiedamounts retains the selenium by acting as an oxidiser. It is preferredthat manganese oxide is included in the additive composition of thepresent invention.

The grey glass composition also includes selenium as an essentialingredient for the grey colour because selenium has a maximum absorptionabout 500 nanometers and also combines with iron oxide to form aniron-selenium complex with a stronger absorption peak at about 490nanometers. Manganese oxide in the Mn⁺³ form also has an absorption peakabout 490 nanometers so that manganese oxide can partially replaceselenium in the composition and provide the absorption needed for thegrey colour of the glass. Selenium can be added to the grey glass in avariety of manners including: the elemental metal and in any compoundform such as sodium selenite, barium selenite, selenium oxide, sodiumselenate, etc. As indicated above it is preferably introduced as theselenite and more preferably zinc or sodium selenite.

Another application of the additive composition of the present inventionis in the manufacture of glass ceramics. An essential feature of glassstructure is that it does not contain crystals. However, by deliberatelystimulating crystal growth in appropriate glasses it is possible toproduce a range of materials with a controlled amount of crystallisationso that they can combine many of the best features of ceramics andglass. Some of these “glass ceramics” formed typically from lithiumaluminosilicate glasses, are extremely resistant to thermal stock andhave found several applications where this property if important,including cooker hobs, cooking ware, windows for gas or coal fires,mirror substrates for astronomical telescopes and missile nose cones.

The invention will now be further described with reference to thefollowing examples, which are illustrative of but not limiting to theinvention.

EXAMPLES Example 1

Preparation Zinc Selenite Additive Composition

A mixture of Polysorbate 20 (Tween 20®) 1 part was dispersed inpolyethyleneglycol 300 10 parts to form a surfactant composition.Calcium carbonate particulate carrier of carbonaceous calcium carbonateof nominal particle size of 2 mm, 98.5 wt % CaCO₃, and less than 0.09 wt% Fe as Fe₂O₃ (Trucal 6® supplied by Tilcon Ltd) (36.76 g) was added toa glass beaker. The surfactant composition (1 g) was added to thecalcium carbonate in the beaker with stirring until an even liquidmixture was obtained. Then zinc selenite (41 wt % Se) (12 g) was addedto the liquid mixture in stages with mixing until a uniform granulebegan to form. Finally the granule was finished by the drop wiseaddition of technical white oil (0.25 g) with mixing until a fullyformed dry granule was produced.

The finished additive composition (granule) contained 9.84% w/wselenium.

Example 2

Preparation of Cobalt II Oxide Additive Composition

A mixture of Polysorbate 20 (Tween 20®) 1 part was dispersed inpolyethyleneglycol 300 10 parts to form a surfactant composition.Calcium carbonate particulate carrier (Trucal 6®) (40.50 g) was added toa glass beaker. The surfactant composition (1 g) was added to thecalcium carbonate in the beaker with stirring until an even liquidmixture was obtained. Then cobalt U oxide (72 wt % Co) (7 g) was addedto the liquid mixture in stages with mixing until a uniform blackgranule began to form. Finally the granule was finished by the drop wiseaddition of technical white oil (0.25 g) with mixing until a fullyformed dry granule was produced. The finished additive composition(granule) contained 10% w/w cobalt.

Example 3

Preparation of Se 1% Formulation

The following ingredients and process were utilised to manufacture theadditive CONTENT IN FINISHED INGREDIENT PRODUCT % W/W Sodium selenite(min. 99.0%) 2.272 Poly ethylene glycol 300 2.008 Polyoxyethylene 20sorbitan 0.201 monolaurate Amorphous precipitated silica 0.291 Calciumcarbonate granule 95.228

The method for 1000 kg batch included the following steps.

In a horizontal ribbon blade solids mixer:

-   1. Switch on the mixer.-   2. Add approximately half of the required calcium carbonate.-   3. Add the sodium selenite.-   4. Mix for 5 minutes.-   5. Add the remaining calcium carbonate granule.-   6. Mix for 5 minutes.-   7. Spray the liquid mixture.-   8. Mix for 5 minutes.-   9. Add the silica-   10. Mix for 3 minutes-   Discharge the mixer.

Example 4

Preparation of Mn containing additives

The following ingredients and process were utilised to manufacture anumber of Mn containing additives (a) 13% Mn CONTENT IN FINISHEDINGREDIENT PRODUCT % W/W CaMg Carbonate 76.5 Poly ethylene glycol 3003.5 Polyoxyethylene 20 sorbitan monolaurate Mixture (10p:1p) MnO 20

(b) 26% Mn CONTENT IN FINISHED INGREDIENT PRODUCT % W/W CaMg Carbonate53 Poly ethylene glycol 300 7 Polyoxyethylene 20 sorbitan monolaurateMixture (10p:1p) MnO 40

(C) 19.5% Mn CONTENT IN FINISHED INGREDIENT PRODUCT % W/W CaMg Carbonate64 Poly ethylene glycol 300 6 Polyoxyethylene 20 sorbitan monolaurateMixture (10p:1p) MnO 30

Method (for 1000 kg batch)

In a horizontal ribbon blade solids mixer:

-   -   1. Switch on the mixer.    -   2. Add approximately half of the required CaMg Carbonate    -   3. Add the MnO    -   4. Mix for 5 minutes.    -   5. Add the remaining CaMgcarbonate    -   6. Mix for 5 minutes.    -   7. Spray the liquid mixture.    -   8. Mix for 5 minutes.    -   9. Discharge the mixer.

Example 5

Preparation of Cobalt containing additive. INGREDIENT Weight ofIngredients (g) Ca Carbonate P10 20600 Poly ethylene glycol 300 625Polyoxyethylene 20 sorbitan monolaurate Mixture (10p:1p) Cobalt Oxide3525 White Oil 250

Briefly, the P10 was mixed for 2 min and then the Polyethyleneglycol300/Polyoxyethylene 20 sorbitan monolaurate, mixture was added andmixing continued for a further 15 min. The cobalt oxide was then addedand mixing continued for a further 15 minutes. Finally the white oil wasadded and mixing was continued for a further 20 minutes to form thefinal additive composition. This composition contained 10 wt % cobalt.

Example 6

Preparation of a selenium containing composition INGREDIENT Weight ofIngredients (g) Ca Carbonate P10 17625 Poly ethylene glycol 300 1000Polyoxyethylene 20 sorbitan monolaurate Mixture (10p:1p) Zinc SeliniteType II 6250 White Oil 125

Briefly, the P10 was mixed for 2 min and then the Polyethyleneglycol300/Polyoxyethylene 20 sorbitan monolaurate, mixture was added andmixing continued for a further 15 min. The zinc selenite was then addedand mixing continued for a further 15 minutes. Finally the white oil wasadded and mixing was continued for a further 30 minutes to form thefinal additive composition. This composition contained 10 wt % selenium.

Preparation of Glass Batches

A number of glass batch formulations were formulated for evaluation ofthe additive compositions of Examples 1 to 3; the glass batchformulations are provided in Table 5. TABLE 6 Sand Soda Ash LimestoneSaltcake Syenite Calumite Selenium Cobalt Cullet TOTAL Typical Batch1000.00 307.08 237.08 13.46 39.58 60.00 0.050000 0.002583 1657.00  25 kgBatch Only 15.09 4.63 3.58 0.20 0.60 0.91 0.000754 0.000039 0.00 25.00250 kg Batch only 150.85 46.32 35.76 2.03 5.97 9.05 0.007543 0.0003900.00 250.00  25 kg Total Batch + Cullet 11.31 3.47 2.68 0.15 0.45 0.680.000566 0.000029 6.25 25.00 250 kg Total Batch + Cullet 113.14 34.7426.82 1.52 4.48 6.79 0.005657 0.000292 62.50 250.00All Weights are in Kg

1. A particulate glass additive composition comprising at least oneparticulate carrier and, deposited on the surface of the carrier orcarriers, at least one additive material in combination with a matrixwhich comprises at least one surface-active agent and/or organic filmforming material.
 2. A composition as claimed in claim 1, wherein thecarrier is inorganic.
 3. A composition as claimed in claim 2, whereinthe inorganic carrier is calcium carbonate.
 4. A composition as claimedin claim 1, wherein the glass additive material is selenium or aselenium containing compound or a mixture of selenium and seleniumcontaining compound.
 5. A composition as claimed in claim 4, wherein theselenium containing compound is a selenite, selenide, selenate.
 6. Acomposition according to claim 4, wherein the selenium containingcompound is a selenite.
 7. A composition as claimed in claim 4, whereinthe selenite is zinc or sodium selenite.
 8. A composition according toclaim 1, wherein the glass additive material comprises a manganese andor a cobalt containing compound.
 9. A composition as claimed in claim 1,wherein the quantity of glass additive material is between 1 and 80% byweight with respect to the carrier.
 10. A composition as claimed inclaim 1, wherein the surface active agent is one or more of monoestersof propyleneglycol and of the food fatty acids, acetic, lactic, citric,tartaric and monoacetyltartaric esters of the mono and diglycerides offood fatty acids, glycerin polyethyleneglycol ricinoleate,polyethyleneglycol esters of soybean oil fatty acids, sorbitanmonostearate, sorbitan tristearate, sorbitan monolaurate, sorbitanmonooleate, sorbitan monopalmitate, propyleneglycol alginate and theirmixtures with polyethyleneglycol and/or with propyleneglycol and/or withglycerin.
 11. A composition as claimed in claim 1, wherein the organicfilm forming material is one or more of methylcellulose,hydroxypropylcellulose, methylhydroxypropylcellulose,hydroxypropylmethylcellulose (HPMC), cellulose acetate phthalate (CAP),carboxymethylcellulose, ethylcellulose, acetylcellulose,Hydroxypropylethylcellulose (HPEC), mixtures of microcrystallinecellulose and carrageenan, polyvinylpyrrolidone, polyvinyl alcohol,polyvinylacetate, gum arabic, substances of wax type such aspolyethyleneglycols, higher alcohols, higher fatty acids andhydrogenated fatty substances, xantham gum, dextrins and maltodextrins.12. A process for the manufacture of a particulate glass additivecomposition which process comprises contacting at least one particulatecarrier with at least one glass additive material to provide a coatedcarrier followed by contact of the coated carrier with one or moresurface active agents and/or one or more organic film forming materialsto form a matrix.
 13. A process for the manufacture of a particulateglass additive composition which process comprises contacting at leastone particulate carrier with at least one surface active agent and/or atleast one organic film forming material to form a mixture andintroducing into the mixture at least one glass additive material toform a additive composition.
 14. A process for the manufacture of aglass additive composition which process comprises mixing at least oneglass additive with at least one surface active agent and/or at leastone organic film forming material to form an additive/surfactant/filmformer mixture and contacting the resulting mixture with at least oneparticulate carrier.
 15. A process as claimed in claim 12 wherein anyone or more process steps are repeated.
 16. A process as claimed inclaim 12, wherein a non-ionic surface active agent is used in a quantityof between 0.5 and 10% by weight with respect to the combined weight ofcarrier and additive material.
 17. A process as claimed in claim 12,wherein said surface active agents are monoesters of propyleneglycol andof the food fatty acids, acetic, lactic, citric, tartaric andmonoacetyltartaric esters of the mono and diglycerides of food fattyacids, glycerin polyethyleneglycol ricinoleate, polyethyleneglycolesters of soybean oil fatty acids, sorbitan monostearate, sorbitantristearate, sorbitan monolaurate, sorbitan monooleate, sorbitanmonopalmitate, propyleneglycol alginate and their mixtures withpolyethyleneglycol and/or with propyleneglycol and/or with glycerin. 18.A process as claimed in claim 12, wherein said organic film formingmaterial is one or more of methylcellulose, hydroxypropylcellulose,methylhydroxypropylcellulose, hydroxypropylmethylcellulose (HPMC),cellulose acetate phthalate (CAP), carboxymethylcellulose,ethylcellulose, acetylcellulose, Hydroxypropylethylcellulose (HPEC),mixtures of microcrystalline cellulose and carrageenan,polyvinylpyrrolidone, polyvinyl alcohol, polyvinylacetate, gum arabic,substances of wax type such as polyethyleneglycols, higher alcohols,higher fatty acids and hydrogenated fatty substances, xantham gum,dextrins and maltodextrins.
 19. A process for the manufacture of glasswhich comprises introducing at least one glass additive compositionaccording to claim 1, into glass forming components as a glass batchbefore addition to a melting furnace or via introduction into themelting furnace during molten glass formation.
 20. A process as claimedin claim 19, wherein the glass batch is for making container orarchitectural or automotive glass.
 21. A process for retarding thevolatilization of selenium used as a decolorant in preparing a containerglass composition comprising including at least one glass additivecomposition according to claim 1, during melt processing of the glasscomposition, said method comprising the steps of: admixing and meltingtogether sand, soda ash, dolomite, limestone, salt cake, a cobaltcontaining compound, and the glass additive composition, in quantitiessufficient to form said container glass composition having a base glasscomposition comprising by weight: 68 to 75% SiO2, 10 to 18% Na20, 5 to15% CaO, 0 to 10% Al₂O₃, and 0 to 5%,K20, 0.002 to 0.025 wt. % cobaltoxide as Co, 0.0010 to 0.0060 wt. % selenium as Se oxides orpolyseleneides.
 22. A selenium and cobalt containing glass obtainable bythe process of claim
 12. 23. A glass batch premix which comprises one ormore additive compositions according to claim 1, and in addition one ormore components required for the manufacture of glass.
 24. A process forthe manufacture of glass which comprises introducing at least one glassadditive composition manufactured by the process of claim 12, into glassforming components as a glass batch before addition to a melting furnaceor via introduction into the melting furnace during molten glassformation.
 25. A process as claimed in claim 24, wherein the glass batchis for making container or architectural or automotive glass.
 26. Aprocess for retarding the volatilization of selenium used as adecolorant in preparing a container glass composition comprisingincluding at least one glass additive composition manufactured by theprocess of claim 12, during melt processing of the glass composition,said method comprising the steps of: admixing and melting together sand,soda ash, dolomite, limestone, salt cake, a cobalt containing compound,and the glass additive composition, in quantities sufficient to formsaid container glass composition having a base glass compositioncomprising by weight: 68 to 75% SiO2, 10 to 18% Na20, 5 tol 5% CaO, 0 to10% Al₂O₃, and 0 to 5%,K20, 0.002 to 0.025 wt. % cobalt oxide as Co,0.0010 to 0.0060 wt. % selenium as Se oxides or polyseleneides.
 27. Aglass batch premix which comprises one or more additive compositionsmanufactured by the process of claim 12, and in addition one or morecomponents required for the manufacture of glass.